[Intel-gfx] [PATCH] Workaround for flicker with panning on the i830

[Thomas Richter]

Am 11.11.2013 16:43, schrieb Daniel Vetter:
> Oh, that's really interesting. gen2 has a unified display fifo on
> machines that support 2 outputs. DSPARB tells the hw how to exactly
> split this up between the two pipes. There are two bit ranges of
> interest here:

/* snip */

Hmm, why I understand *that* it does make a difference, I do not 
understand the details.
By a unified display fifo do you mean that the display output has an 
internal buffer memory (the fifo) which
basically feeds the the DVOs or the LVDS with memory, which comes via 
DMA into the fifo. Is that right?

By "split", do you mean that a fixed amount of bytes (or rather, lines 
as in multiples of 16 bytes) are allocated for each
participating pipe?

Simply enlarging the fifo does not help (i.e. writing a larger value 
into the register). Just the positions where I get the flicker change, 
but the problem does not go away. So whatever needs to be done is to 
adjust this register according to the alignment of the base address of 
the corresponding DMA engine that feeds the pipe.


> What we'd need to do here is to update this register when switching
> the number of active display pipes in the ->modeset_global_resources
> hook. We also need to make sure we have updated watermark values set
> up already, before rewriting the value of DSPARB (since the watermarks
> depend upon the size of the fifo).
>
> For I start I'd go with splitting the fifo according to the display
> clock between plane A and B and giving nothing to plane C. We don't
> have any code to use plane C so giving everything to just A and B is
> better.

By that you mean "BEND = maximum" and "AEND" in between? That does not 
seem to be sufficient. It needs to be modified according to the buffer 
alignment, and sometimes smaller values work, sometimes larger ones.

Greetings,
     Thomas